1. Technical Field
Embodiments of the present invention relate to a printing apparatus.
2. Related Art
A large format printing apparatus is configured with a so-called roll-to-roll system which supplies a long medium as a paper roll, and, using a winding unit, winds and collects the medium that is transported by a transport unit and that is subjected to printing by a printing unit. The printing apparatus is also provided with a tension application unit that generates tension in the medium between the transport unit and the winding unit in order to cause the medium to be stably wound onto the winding unit. For example, JP-A-2013-22744 discloses a recording apparatus (a printing apparatus) which is provided with a tension application mechanism that includes a tension application member and a pair of arm members which support the tension application member, and that applies tension to a band-shaped medium. The tension application mechanism is provided with an upper limit sensor which obtains the upper limit of an inclination angle of an arm member and a lower limit sensor which obtains the lower limit of the inclination angle. The winding of the medium onto the winding unit is controlled by these sensors, and tension within a predetermined range is caused to act on the medium by causing the tension application member to rock in a fixed angular range.
However, in the printing apparatus described in JP-A-2013-22744, the center of gravity position of the tension application unit is concentrated on a tension bar (the tension application member). In order to keep the tension which is caused to act of the medium between the transport unit and the winding unit within the predetermined range, it is necessary to narrow the angular range (the rotational range) in which the tension bar is caused to rock or move. As a result, it is necessary to repeat the transportation and the winding of the medium. In addition to the tension of the tension application unit, a tension that is generated by the driving force when winding the medium onto the winding unit also acts on the medium. In a transport path from a transport roller of the transport unit which transports the medium to the winding unit, in a case in which there is a difference in the transport path length from one end side of the transport roller to one end side of the winding unit and the transport path length from the other end side of the transport roller to the other end side of the winding unit, slack arises in the medium on the short side of the transport path, and a high tension is generated unevenly on the long side of the transport path. When the winding unit is driven in this state, an unbalanced force is generated in the winding unit, and a force couple is generated in the winding unit. The force couple is centered on the end portion of the short side of the transport path such that the side on which the transport path is longer rotates. Due to this force couple, the tension is concentrated obliquely on the end portion of the short side of the transport path in the transport roller from the end portion of the side at which the transport path is long in the winding unit. When a pulling force to the downstream side in the transport direction arises on the side at which the tension is concentrated becomes greater than the friction force between the medium and the transport roller, the medium of the side at which the tension is concentrated (i.e., the short side of the transport path) slides to the downstream side in the transport direction, and a vicious cycle in which the slack of the medium is further increased is repeated. Due to the increasing slack, twisting and wrinkling may eventually arise in the medium which is wound onto the winding unit.